Alcohols and Phenols
Chapter 17
Alcohols
nClassification
nPrimary RCH2OH
nSecondary R2CHOH
nTertiary R3COH
Review
Preparation
n
Hydration of Alkenes
n Markovnikov’s Rule
n Carbocation mechanism
Review
of Preparation
n Oxymercuartion demercuaation
•
Follows Markovnikov’s
Rule
Review
of Alcohol Preparation
n 
Hydroboration-Oxidation
n Anti-Markovnikov addition
n cis-Addition
Review
of Alcohol Preparation
n Hydrolysis of Alkyl halides
RX + OH- à ROH + X-
n E2 elimination can occur with
OH-
(CH3)2CH2CH2Br + OH- à (CH3)2CH2CH2OH + Br-
n SN2 on primary halides and OH-
n SN1 on tertiary halides and H2O
Nomencalture
n Select the longest chain
containing the carbon bearing the OH group.
n Use the hydrocarbon name but
drop the “e” and add “ol”.
n Number from the end on the
chain that will give the OH the lowest number
Nomenclature
Examples
n Name the following
Special
Names
n 
Benzyl, allyl,
glycols, phenols
Industrial
Preparations
n Methanol
CO + 2H2 à CH3OH
n Ethanol
CH2=CH2 + H3O+ à CH3CH2OH
Industrial
Preparations
n 
Ethylene glycol
n Used in polyester and
anti-freeze
Hydorgen
Bonding
n 
Boiling points higher than
hydrocarbon of same molecular weight.
M.W. B.P.
n CH3CH3 30 -88.6
n CH3Cl 50.5 -24
n CH3OH 32 +64
Alcohols
and Acids and Bases
n
Alcohol as a base
Alcohols
and Acids and Bases
n Alcohols as acids
n Dilute aqueous solution
ROH + H2O
ó RO- + H3O+
n Low pK2’s strong acids
Alcohols
and Acids and Bases
n pKa’s of alcohols
n R3COH 18
n R2CHOH 17
n RCH2OH 16
n CH3OH 15.54
n CF3CH2OH 12.43
n (CF3)3COH 5.4
Rationalization
for acidity of (CF3)3COH
n Inductive effect
(CF3)3COH + H2O ó (CF3)3CO- + H3O+
Predicting
Equilibria
n 
Which direction would
the equilibrium lie?
Preparation
of Alcohols
n Alcohols represent a key
intermediate compound type for reaction sequences
n They can be prepared from
many starting materials and are converted into many other functional groups
Reduction
of Carbonyl Compounds
n
Aldehydes and Ketones
n Most common NaBH4 or LiAlH4
n
Less common H2 and catalyst: Pt, Pd/C, or
Ni
Sodium
Borohydride
n Less reactive than LiAlH4,
therefore, more selective.
Lithium
Aluminum Hydride
n
Very reactive, less
selective than NaBH4
Selective
Reductions
n
NaBH4 will
reduce ketones, but not esters.
n LiAlH4 will
reduce BOTH ketones and esters.
Selective
Reductions
n
NaBH4 and
LiAlH4 do not reduce double bonds.
Mechanism
n Similar mechanisms
n Hydride (H-) transfer
Metal
Hydrides and Water
n LiAlH4 reacts explosively
LiAlH4 + H2O à LiAl(OH)4 + H2
+ heat
n NaBH4 reacts rapidly in acid
solution, slowly in basic solution
NaBH4 + H2O à NaB(OH)4 + H2
•
Slow
in basic solution
•
Fast
in acid solution
Catalytic
reduction
n Not used much, but does
occur
n
Metal hydrides have
replaced this method
Organometallics
Reactivity depends on
the metal
n Li, Na, Cu, others
n Mg is the metal of “Grignard
Reagents”
Grignard
Reaction
n
The ether must be DRY!
n
Ether is involved in
the Grignard reagent as a complex
Grignard
Reaction + Acid
n 
An acid such as water
replaces metal with H
The
Grignard Reaction
Reactions
of Grignard Reagents
n With ketones and aldehydes
Planning
a Synthesis
n Primary alcohols
Secondary
Alcohols
n RMgX and Aldehydes
Tertiary
Alcohols
n 
Grignards with ketones
Reaction
with Esters
n Special tertiary alcohol
synthesis
n Two groups the same
What would
you use to make each of these?
Reactions
of Alcohols
n Breaking the OH bond
n
This is the acid reaction alcohols
RO-H à RO- + H+
n
Alcohols have pKa’s about the same as water or just slightly greater
Reactions
at the C-O Bond
n So these reactions we’ve
seen
n 
Dehydration
Mechanism
n
Carbocation mechanism,
E1
Rate
of dehydration
n Follows carbocation
stability
n R3COH > R2CHOH >
RCH2OH
Other
Dehydration Reagents
n
Phosphorus
Osychloride, POCl3
n
E2 Mechanism
Alkyl
Halides
n
SN1 –
Carbocation mechanism 3° > 2°
> 1°
Thionyl
Chloride
n
Often better with 1°
Phosphorus Trihalide
n
PBr3 and
PCl5 are also useful
Tosylates
n 
Makes OH a better
leading group
n
TsO- is as
good as Cl- as a leading group.
Oxidation
of alcohols
n
Primary alcohols are
first oxidized to aldehydes and the aldehyde to an acid if water is present
Oxidation
of Alcohols
n
Secondary alcohols
oxidized to ketones
Oxidation
Conditions
n
Jones reagent CrO3, H2SO4, H2O, acetone
n
Best for secondary
alcohols
n
Chromic acid can also be used
n
Chromic acid H2CrO4 (Na2Cr2O7/H2SO4/H2O)
Oxidation
Reagents
n
Pyridinium
Chlorochromate (PCC)
n Oxidation under anhydrous
conditions
Oxidation
Mechanism
n 
Not all the details
(yea, sure!)
Alcohol
Protection
n 
Often you want to do
reactions that will affect the -OH Group.
You need to protect the group during these reactions and then regenerate
the -OH
Example
Phenols
n
The hydroxyl group is
a strongly activating –o, -p director making phenols very reactive.
Phenol
Oxidizes to Benzoquinine
Reduction
of Benzoquinone gives Hydroquinone
Spectra
of Alcohols
n IR Alcohols and Phenols
n The OH stretch at 3300 –
3600 cm-1
n The CO stretch at 1000 –
1200 cm-1
n Phenols show additional
aromatic peaks at 1500 cm-1 and 1600 cm-1
The OH stretch is
very broad due to hydrogen bonding.
Spectra
of Alcohols
n Carbon NMR
C to which O is
attached ~50-80 ppm
b Carbon ~30 -
40 ppm
Spectra
of Alcohols
n Proton NMR
n H attached to oxygen .5 – 5
ppm (anywhere!)
n H attached to the carbon
where the OH is attached 3.5 – 4.5 ppm.
Spectra
of Alcohols
n Mass Spectra
a Cleavage
Dehydration
